IFT, Intraflagellar Transport, discovered in Chlamydomonas in our laboratory, is essential for the assembly and maintenance of almost all eukaryotic cilia and flagella. Studies of the genes involved in IFT and its mechanism have led to new findings on the role of cilia/flagella (interchangeable terms) in many pathologies where the role of cilia was heretofore unsuspected. Because ciliary signaling processes, and their receptors on the ciliary membrane, are key to many of these pathologies, the proposed research is directed at determining how channels/receptors are targeted to the flagellar membrane, and to the flagellar axoneme through a proposed flagellar pore structure, and how IFT is involved in this transit process. We will determine, for the first time, the high resolution ultrastructure of the IFT particles both in situ and as isolated particles with Cryo-EM. Because there is mounting evidence, from our laboratory and others, that the cilium is involved in the control of the cell cycle, one of our most important goals is to determine the molecular interactions between one of the IFT polypeptides, a small G protein, and the cell cycle. Finally, one of our initial aims, 40 years ago, in establishing systems of cilia and flagellar regeneration, was to study how the cell recognizes the lack of its flagella and up-regulates hundreds of genes rapidly after flagellar detachment; we will determine what cytoplasmic factors are responsible for this transcriptional up-regulation. PUBLIC HEALTH RELEVANCE: This proposal extends our study of intraflagellar transport (IFT) and how this motility process participates in the assembly and maintenance of eukaryotic cilia/flagella. Studies on the genes and mechanisms underlying IFT have led to new insight into the role of cilia in many pathologies where this role was heretofore unsuspected. Among these are situs inversus, retinal degeneration, developmental diseases of bone, muscle and connective tissue, cystic diseases of the kidney, liver and pancreas, as well as syndromes that include obesity and diabetes. The proposed research is directed at basic cell and molecular aspects of IFT which have not yet been well-researched.